1. From the test—fat-percentage—of the rich cream subtract the test desired.
2. From the test desired subtract the test of the milk used for diluting.
3. Divide the first difference by the second, and the result will be the number of pints (or pounds) of milk to be added for each pint (or pound) of the rich cream.
For instance, you may want to thin some 30% cream to 10% for making ice cream. The milk to be added is skim milk. Then:
1. 30 - 10 = 20.
2. 10 - 0 = 10.
3. 20 divided by 10 = 2. So for each pint of rich cream you may add 2 pints of skim milk.
Or you may wish to thin the 30% cream with whole milk, which has 4% butter-fat. Again:
1. 30 - 10 = 20.
2. 10 - 4 = 6.